Contact inhibition of division: Involvement of the electrical transmembrane potential

Abstract Measurements of simultaneous mitotic activity, electrical transmembrane potential (E m ), and cell density levels in both 3T3 and Chinese hamster ovary (CHO) cell cultures reveal that a 5‐ to 6‐fold increase in the E m level is associated with development of mitotic arrest at saturation densities. This rise occurs both in confluent monolayers and in interior areas of isolated colonies, and is independent of the rate at which confluence is attained. The E m rise is accompanied by a substantial decrease in intracellular Na. Electron microscopy of saturated CHO monolayer sections shows from 46 to 63% of the cell surfaces to be in close apposition (<300 Å spacing). These results for contact inhibited cultures support the hypothesis that mitotic activity may be functionally coupled with the E m level and associated ionic concentration levels. It is suggested that contact inhibition of mitosis may result from a reduction in synthesis of mitogenically essential RNA following a decrease in intracellular Na produced by contact‐induced alteration of surface ion‐transport activity.